Engine wont start - no fuel pressure

[McRat]

LLY's have very similiar fuel systems functionally as LB7's.

Do you have a lift pump? If so, what kind of pressure do you see at the inlet of the CP3's?

 

[mick]

Sounds like somethings blocked, but like Pat said try starting with the CP3 un plugged

Tried thanks Paul

 

[mick]

What does it do if you try to start it with the CP3 unplugged?

Same as before pressure at app 200-230

 

[mick]

LLY's have very similiar fuel systems functionally as LB7's.

Do you have a lift pump? If so, what kind of pressure do you see at the inlet of the CP3's?

Washes my engine down plenty of fuel there

 

[McRat]

I wonder if you have a single bad injector that is stuck open, and not allowing rail pressure to build. This has happened to others in the past.

 

[McRat]

The only way I can think to test this is a PITA.

Remove each injector, and take one of the metal lines and hook it to the back of the HP outlet on the secondary CP3. Crank the engine and see if fuel comes out. It should not.

 

[Mike]

hmmmm..... Good question...

 

[mick]

Sounds like something is blocked or pinched. A trickle ain't good.[/QUOTE]


Like how much fuel should come out the return line?. after cranking it 3 times for 7-8 sec each I had about 2 teaspoons of fuel

 

[McRat]

I remember it as being more than that. But it does indicate there is fuel going through the CP3.

 

[mick]

The only way I can think to test this is a PITA.

Remove each injector, and take one of the metal lines and hook it to the back of the HP outlet on the secondary CP3. Crank the engine and see if fuel comes out. It should not.

Probably not as big of PITA as not running as it is now. At the FRP sensor I am recieving 5 volt at the 5 volt ref .01v at the low ref and 5 volts at the middle wire (sensor) Is that normal?

 

[McRat]

Here's basically how your fuel system works:

The CP3 has lift pump in the back, that is a fixed displacement gear-style, like an oil pump. This rotates at crank speed any time the engine turns. A regulator is mounted in the back near the gear pump, which closes when you apply current to it. When it closes, most all the fuel returns to the tank. When you remove current, some of the fuel goes into the 3 high pressure piston bores in the body. The crank in the CP3 pressures this fuel as it rotates at engine speed. The high pressure fuel goes out the metal line and into the rails, first the driver's rail, then a cross-over tube feeds the passenger rail (this contains a .75mm restrictor). HP fuel is now at all the injectors. When the injector gets power, it retracts the needle, and allows fuel to spray in the cylinder. When power is removed, the trapped fuel is allowed to go out the return line so the needle can return to the closed position. If one of the check balls is missing or stuck, the HP fuel can go straight into the return. This can keep the rail for any of the cylinders from reaching high pressure. Volume does not change, just where the fuel goes.

 

[McRat]

Probably not as big of PITA as not running as it is now. At the FRP sensor I am recieving 5 volt at the 5 volt ref .01v at the low ref and 5 volts at the middle wire (sensor) Is that normal?

Low ref is ground.

Not sure whether 5v is full pressure, or no pressure. I don't have access to GM right now.

But I'm pretty sure the engine will start without the rail pressure sensor plugged in.

Let's move this to Hard Parts, and see if someone knows.

 

[mick]

Here's basically how your fuel system works:

The CP3 has lift pump in the back, that is a fixed displacement gear-style, like an oil pump. This rotates at crank speed any time the engine turns. A regulator is mounted in the back near the gear pump, which closes when you apply current to it. When it closes, most all the fuel returns to the tank. When you remove current, some of the fuel goes into the 3 high pressure piston bores in the body. The crank in the CP3 pressures this fuel as it rotates at engine speed. The high pressure fuel goes out the metal line and into the rails, first the driver's rail, then a cross-over tube feeds the passenger rail (this contains a .75mm restrictor). HP fuel is now at all the injectors. When the injector gets power, it retracts the needle, and allows fuel to spray in the cylinder. When power is removed, the trapped fuel is allowed to go out the return line so the needle can return to the closed position. If one of the check balls is missing or stuck, the HP fuel can go straight into the return. This can keep the rail for any of the cylinders from reaching high pressure. Volume does not change, just where the fuel goes.

Thanks for spending the time there Pat

 

[WolfLMM]

I would say you have a hung injector.

 

[mick]

I would say you have a hung injector.

You are the 2nd one to say it. Looks like I may have to start the PITA process of elimination on the injectors. Thanks

 

[McRat]

Hey.

Try this:

Unplug all injectors. Remove the little clips that hold on the return tubes on the top of each injector, and pull off the lines. Now crank the engine. None of the injectors should return fuel if my thinking is correct. If one does, BINGO, you found your villain.

To prove the point, figure out a way to block off that one injector line, and see if the engine starts. It should.

 

[JoshH]

I have a couple of fittings that are the same thread as the nipples on the fuel rail and a little steel ball that goes in it to block off fittings. I got them with my dual CP3 setup so I could take the second CP3 off line in the event that it had a problem. I think you should be able to source some fittings somewhere and a check ball as well.

 

[bullfrogjohnson]

Why not just pull the glow plugs and unplug the FICM and crank the motor. If you have a hung injector the fuel will be coming out of the glow plug hole.

 

[LBZ]

Why not just pull the glow plugs and unplug the FICM and crank the motor. If you have a hung injector the fuel will be coming out of the glow plug hole.

Beat me to it. X2 on the pulling the glow plugs. If your injectors have been sitting for awhile, the old fuel in them can gum them up as there is lots of bacteria in diesel fuel.

 

[mick]

Hey.

Try this:

Unplug all injectors. Remove the little clips that hold on the return tubes on the top of each injector, and pull off the lines. Now crank the engine. None of the injectors should return fuel if my thinking is correct. If one does, BINGO, you found your villain.

To prove the point, figure out a way to block off that one injector line, and see if the engine starts. It should.

Thanks Ill try that one tomorrow Pat and let you know